In the past, technological advances in the treatment of sewage have been directed for the most part to the various processes utilized in the reduction of raw sewage, such as aeration, settling coagulation, chemical precipitation of metallic ions, etc. The end products of all such sewage from water treatment facilities, however, are a clear effluent and waste sludge. This invention is directed particularly to novel and innovative means for the handling, processing, dewatering and disposal of such sludge in an efficient and economical manner.
The first requirement in sludge handling is to reduce moisture, and to increase handling ability by reducing volume. The process is usually referred to as concentration, thickening, dewatering or drying, according to the amount of moisture being removed. Different sewage and water treatment processes yield sludges of different solids concentrations ranging approximately from 2 to 20 percent. Further moisture reduction may be desirable to 25% solids for some types of mechanical handling. Higher solids content may be desirable for specific uses or disposal methods.
Existing sludge dewatering equipment falls primarily into two categories (1) simple and inexpensive, but slow, sand drying beds; and (2) fast, but expensive, highly mechanized devices such as presses, vacuum filters, centrifuges, heat dryers and incinerators.
Because of the increase in the separation of both free and bound water from the sludge solids effected by the instant invention, a 200% savings is realized in the area of land required for the dewatering process, and further savings in the operating and maintenance costs of sludge processing and utilization are experienced. No other sludge dewatering system is more cost effective and efficient in continued operation.
Sand drying beds require up to seven weeks to achieve cake concentrations of 25 to 40 percent. The slowness of this method requires bed areas ranging from 1 to 3 square feet per capita of population served, depending on sludge quality and climate conditions. The extensive land requirements of such systems have commonly forced plants serving more than 30,000 persons into mechanical equipment. Sand beds are, however, used by 38 percent of cities serving populations over 100,000.
The disadvantages of mechanical equipment stem from its high initial cost, high maintenance and operational costs, frequent breakdown problems and large energy consumption.